In recent years, many portable electronic devices such as video cameras with video tape recorders, portable telephones, laptop computers, etc. have been produced and they have been made compact and light. A study and development for improving the energy density of batteries, especially, secondary batteries as the portable power sources of these electronic devices have been actively advanced. Particularly, since nonaqueous electrolyte secondary batteries such as lithium-ion secondary batteries can obtain energy density higher than those of lead-acid batteries and nickel-cadmium batteries as conventional aqueous electrolyte secondary batteries, the nonaqueous electrolyte secondary batteries are useful as the power sources of the electronic devices.
As a negative material used for such a lithium-ion secondary battery, carbonaceous materials such as non-graphitizable carbon or graphite have been widely employed, because they have a relatively high capacity and show good cyclic characteristics.
As the high capacity of the lithium-ion secondary batteries is realized, the carbonaceous materials to act as an anode further need to have higher capacity. For example, Japanese Patent Application Laid-Open No. HEI 8-315825 proposes that carbonizing materials and manufacturing conditions are selected to achieve a high capacity by the carbonaceous materials. In the above-described carbonaceous materials to act as an anode, since an anode discharging potential is 0.8 V to 1.0 V relative to lithium, battery discharging voltage when a battery is formed becomes low, so that a great improvement of the energy density of the battery is not anticipated. Further, the carbonaceous anode materials are disadvantageously large in its hysteresis in the form of a charging and discharging curve and low in its energy efficiency in each charging and discharging cycle.
As an anode having a high capacity, there have been proposed materials produced by applying a process that a certain kind of metal is electrochemically alloyed with lithium and the alloy is reversibly combined/decombined. As such materials, there may be exemplified, for instance, Li—Al alloy, etc. Further, Si alloys such as Li—Si alloy are disclosed in the specification of U.S. Pat. No. 4,950,566. A battery using the Li—Al alloy and the Li—Si alloy as negative materials exhibits disadvantages that the expansion and contraction of an anode upon charging and discharging operations are terrible, the negative material is caused to be minute every time charging and discharging cycles are repeated and cyclic characteristics are seriously bad. As one of main factors that the cyclic characteristics are deteriorated, it may be guessed that the negative materials are caused to be minute so that the electronic connection between the negative materials or the negative materials and a current collector is prevented to hardly advance charging and discharging reactions.